工程跑SDK6.1的时候很正常，但今天跑了一下SDK5.1就出现问题了：
dyld: lazy symbol binding failed: Symbol not found: _objc_setProperty_nonatomic_copy
Referenced from: /Users/xxx/Library/Application Support/iPhone Simulator/5.1/Applications/8BB5CBD7-DAE9-4189-B76F-E682BC95746F/xxx.app/xxx
Expected in: /Applications/Xcode.app/Contents/Developer/Platforms/iPhoneSimulator.platform/Developer/SDKs/
iPhoneSimulator5.1.sdk/System/Library/Frameworks/Foundation.framework/Foundation
一开始不知道问题出在了哪里，找了半天才发现是静态库的target不对，只要将静态库的target改成5.1，再跑5.1的时候就好了。
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